Our objective is to determine the thermodynamic properties of reactions between gaseous ligands and abnormal or unusual hemoglobins. These properties include changes of enthalpy, entropy, free energy, heat capacity. Bohr protons, and allosteric effector molecules upon ligation. Direct calorimetric measurements using a gas microcalorimeter are being made on the reaction between CO and Hb M Iwate in its half-reduced state over a pH range of 5.5 to 9.0 in the presence and absence of inosotyl hexaphosphate (IHP) in order to determine the influence of structural changes upon the IHP binding site. Direct IHP to hemoglobin heat titrations complete the necessary set of measurements to test for thermodynamic consistency. Comparable results are obtaind on Hb A. Calorimetric measurements of ligand binding as a function of extent of reaction are contemplated for Trout Hb IV as a comparative study to results obtained on Trout Hb I. BIBLIOGRAPHIC REFERENCES: Heats of Carbon Monoxide Binding by Hemoglobin M Iwate H. T. Gaud, S. J. Gill, B. G. Barisas, and K. Gersonde Biochemistry (1975), 14, 4584-9.